Dithered high resolution images of a supermassive binary black hole candidate SDSS J153636.22+044127.0 will be obtained with the WFPC2/PC in F675W. This QSO was identified in November, 2008 by a principal components analysis of the ~ 17,500 QSOs in the SDSS DR7 sample. It is unique among all known QSOs in having two broadline regions, indicative of two supermassive black holes being actively fed. It is the best candidate for a supermassive binary black hole known. Such binaries should be common in the Universe and play key roles in the formation and evolution of galaxies, yet no convincing examples had been identified prior to this QSO. The HST imaging should be able to constrain two alternative hypotheses that this object is 1) the site of a black hole ejected from a nucleus by a multi-body interaction, or 2) a simple line of sight superposition of two unrelated AGN. With the superb spatial resolution of HST, two AGN separated by > 300pc (projected) should be readily visible.

The observational goal is to test if the QSO is a pure point source. We will conduct F675W imaging in the PC1 CCD of WFPC2. The observations will be dithered in a 2X2 pattern of 0.5 pixel steps (with a CR-split at each position) to provide a Nyquist-sampled superimage. The final resolution should be ~0.06'' FWHM. The F675W bandpass covers H-beta for both redshift systems, as well as the [O III] lines of the r-system. With the left-over time in the orbit, we have added a single CR-split F439W exposure to add color information and to provide slightly better resolution. AGN/QUASARS 0 false 0.0 0.0 false false false false false SUPPORTED GALAXY QSO QUASAR AB(675W)=16.73 J2000 15 34 6.9530 +04 51 18.37 J2000 WFPC2 Imaging No F675W POS-TARG DITHER 0.559017 LINE 0.559017 false false 143.130102 4 26.56505 WFPC2-BOX 1 false The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 11993 :visit-id "01" :proposal-version -1 :trans-version "20090130" :date "06-Feb-2009 10:03:41.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 448160 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11993 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11993 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2580 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) true 1 0